I. Field of the Invention
This invention relates to a system useful for the separation of liquid and gas, and more particularly to a medical device, such as a blood oxygenator or a cardiotomy reservoir, which employs a defoamer system that, in one embodiment, affords excellent separation of macroscopic and microscopic air from blood while at the same time minimizing blood path contact with the silicone containing compounds typically used in the defoamer.
II. Description of the Prior Art
There are many systems known in the art which are used to remove gas (such as air) from fluids and which also employ a defoamer assembly in such systems. For example, in various types of surgical procedures, it is often necessary to perform a treatment whereby the patients blood is subject to a bypass flow outside of the patient's body, and an apparatus such as an oxygenator is employed In many such oxygenators, oxygen is transferred to the blood via a procedure which forms a foam and therefore requires a defoamer assembly.
These oxygenators are used in open-heart surgery and other operations and treatments of the body when it is necessary to establish an extracorporeal circulation system for temporarily assuming the functions of the heart and lungs of the patient. In such a system, the oxygenator operates to perform the function usually performed by the lungs of the patient, i.e., the life-supporting transfer of oxygen into the blood and carbon dioxide out of the blood. The oxygenator is used in association with a pump which performs the function of the heart to cause circulation of the blood. Thus, early versions of the oxygenator were often referred to as "heart-lung" machines The early heart-lung machines were typically rotating discs which passed through a pool of blood, but were only partially immersed therein such that the free surface of the disc exposed the blood to oxygen and accomplished some gas transfer. After this, bag-type oxygenators were introduced which were superior to the disc oxygenators, but which left much to be desired.
At the present time two principal types of blood oxygenators are used which have proven highly efficient, provide minimal blood trauma, are convenient to set up and operate, are cost effective and have provided excellent clinical results, i.e. bubble oxygenators and membrane oxygenators. In a membrane oxygenator, a thin, highly gas permeable membrane is placed between the gas and blood. Venous blood flows along one side of the membrane and gas is on the other side. A pressure gradient is established so that when the partial pressure for oxygen is higher in the ventilating gas than the partial pressure for oxygen in the venous blood, oxygen will diffuse across the membrane into the blood. Bubble oxygenators simply diffuse gas bubbles into venous blood. The oxygenated blood is typically defoamed before it is ready for delivery to the patient.
In medical devices such as the oxygenators as described above, and in other medical devices such as cardiotomies and hardshell venous reservoirs, air or some other gas can be introduced into the blood, e.g. oxygen (in an oxygenator), nitrogen, carbon dioxide, etc. Typically, when this occurs it is medically necessary to remove certain gas from the blood prior to the blood going to the patient. Separation of the blood from the gas requires the medical device to be used in combination with a defoaming device which typically incorporates some sort of an agent to assist in breaking the foam down. In medical applications, about the only agent that has proved acceptable is a silicone antifoam agent. However, in the process of the silicone agent performing its job, i.e. remove the gas from the blood, a small amount of the silicone actually is transferred into the blood. The problem with this is that silicone is not metabolized by the human body, and therefore silicone accumulates in the body. Even though silicone is an inert material it is undesirable within the human body, under some circumstances, because it can tend to clog up some of the very small capillaries and arteries within the human body.
As described herein, the features of the present invention can be employed in various types of medical devices. Examples of the type of so-called membrane oxygenators which can employ the features of the present invention are described in U.S. Pat. Nos. 4,094,792 and 4,196,075 both of which are assigned to Bentley Laboratories, Inc., the assignee of the present invention. In addition Bentley Laboratories, Inc. products identified as the Bentley BCM-3 and BCM-7 integrated membrane oxygenators which are oxygenators having three major components can incorporate the defoamers of the present invention. Examples of the bubble type blood oxygenator that can employ the features of the present invention are described in U.S. Pat. Nos. 3,468,631, 3,488,158 and 3,578,411, the last two of which describe devices which have come to be known as the Bentley Oxygenator, and also U.S. Pat. Nos. 4,282,180 and 4,440,723, both assigned to Bentley Laboratories, Inc.
Various prior art examples of blood oxygenators and gas-liquid type of transfer apparatus are described in U.S. Pat. Nos. 3,065,748; 3,256,883; 3,493,347; 4,073,622; 4,138,288; 4,182,739; 4,203,944; 4,203,945; 4,288,125; 4,231,988; 4,272,373; 4,336,224; 4,370,151; 4,374,088; 4,396,584; 4,407,777; 4,440,722; 4,493,692 and 4,533,516.